I once heard an interesting idea to implement not a per-player weight-limit, but a per-team weight limit. The average weight of the Seahawks (my home team) active roster this year is 246 lbs. So, for the sake of example, maybe shave 7-8% off of that and say that the 11 guys on the field for any given play can't weight more than 2,500 lbs combined.

That would give teams a bit of wiggle room to use huge linemen if they want to, though the tradeoff is smaller ball-handling players.